David Shayler, who is from Middlesbrough, is an ex-MI5 agent, who was convicted of breaking the Official Secrets Act.

Back in 1997 David Shayler left the Intelligence services after six years and leaked secret documents to the Mail on Sunday newspaper claiming he had a public duty to expose malpractice within the security services.

The documents suggested that the government kept secret files on politicians who had gone on to be cabinet ministers.

Shayler was arrested in France and held without charge for nearly four months in a Paris jail. Meanwhile the UK's attempts to extradite Shayler were rejected by a French court.

In July 2000, David Shayler's novel, The Organisation, was passed by the government censors. Described as "a gritty thriller about spies, sex and football", Shayler wrote it while living in France.

A month later David Shayler was charged under the Official Secrets Act within hours of arriving back in Britain.

In March 2002 the House of Lords rejected any use of a public interest defence in Shayler's trial. In November, David Shayler was found guilty on three counts of exposing official secrets and sentenced to six months imprisonment, although he served less than seven weeks.

David Shayler had put his name forward to stand against Tony Blair in the Sedgefield Constituency during the 2005 General Election, however on April 17 2005, David Shayler stood down in favour of Reg Keys, saying:

"If Reg can beat Blair, then they'll be dancing in the streets of Baghdad and Kabul as well as large parts of Britain. It will be a 'World Portillo Moment', just like when Tory MP Michael Portillo lost his Enfield seat in the 1997 General Election and people spontaneously ran into the streets laughing and dancing."